Solid state image pickup apparatus with shutter signal and overflow drain

ABSTRACT

A solid-state image pickup apparatus employing a frame interline transfer type solid-state image sensor. The operation of a driving circuit is controlled by a controller in such a manner that image pickup charges produced by photosensitive elements are drained in a charge draining section at a drain timing during a vertical blanking period, and image pickup charges produced by the photosensitive elements in an image pickup unit after lapse of a predetermined light exposure period since the drain timing are transferred to a vertical transfer register so as to be transferred by high speed transfer from the image pickup unit to a storage unit during the next vertical blanking period so that the image pickup charges are read out line sequentially during the imaging period via horizontal transfer registers. The apparatus maintains a constant start timing of the effective light exposure period and produces video signals synchronized with external synchronization signals.

BACKGROUND OF THE INVENTION

This invention relates to a solid state image pickup apparatus employinga frame interline transfer type solid state image sensor and, moreparticularly, to a solid state image apparatus having the function of aso-called electronic shutter.

A solid state image sensor such as CCD (charge coupled device) imagesensor, has advantageous features such that it is free of burning orresidual images as compared to an image pickup tube device, it is highlyshock-proof, and lends itself to miniaturization of video cameras. Invideo cameras conforming to the standard television systems, such asNTSC systems employing an interlace scanning system, a CCD image sensoris employed in which image signals from pixels of odd-numbered fieldsand those from pixels of even-numbered fields are read out alternatelyat intervals of one-field periods (one-sixtieth of a second in the caseof the NTSC system).

The solid state image sensor, such as the above-described CCD imagesensor, may be classified, according to the type of the transferstructure used for outputting image pickup electrical charges, into aframe transfer type, interline transfer type and a frame interlinetransfer type. In the interline transfer type CCD image sensor, forexample, one-field image pickup charges, produced by the photosensitiveelements, are transferred at intervals of one-field periods to verticaltransfer registers by sensor gate pulses so as to be read outline-sequentially from the vertical transfer register via horizontaltransfer registers.

On the other hand a so-called progressive scan CCD or PS CCD imagesensor, in which a horizontal transfer gate for two horizontal lines isprovided so that image pickup signals from pixels of odd-numbered fieldsand those from pixels of even-numbered fields are read out in theirentirety during a one-field period, has been presented for use inhigh-resolution video cameras, such as in high-vision televisionsystems.

Besides, there is also presented a CCD image sensor of the type havingthe function of an electronic shutter for controlling effective chargestorage periods of the photosensitive elements electronically. With theCCD image sensor having the function of the electronic shutter, ashutter control pulse is applied to its substrate for sweeping out imagepickup charges of the photosensitive elements in an overflow drain forcontrolling the light exposure time, that is the effective chargestorage period, as shown in FIG. 4. In this figure, a shutter controlpulse φSP_(1/1000) which will give an effective charge storage periodT_(1/1000) of a duration of 1/1000 second, and a shutter control pulseφSP_(1/700) which will give an effective charge storage period of aduration of 1/700 second, are shown. Time intervals beginning at t₁ andt₂ and ending at t₀, the time of the first one of the sensor gate pulsesφSG, yield effective storage periods T_(1/1000) and T_(1/700),respectively.

In the conventional CCD image sensor, having the function of theelectronic shutter, the end timing of the effective charge storageperiod or the effective exposure period is the timing ± of the sensorgate pulse φSG, such that the end timing of the effective light exposureperiod is constant for any shutter speed, with the start timing of theeffective exposure period being changed with the shutter speeds.Conversely, with shutter control of a mechanical optical shutter in anoptical camera employing a halide film, light exposure is started onactuation of a shutter release so that light exposure is terminated at atiming associated with the shutter speed.

The electronic shutter control in the CCD image sensor is related in aninverse fashion with the shutter control in the optical shutter in anoptical camera, so that, in a solid state image pickup device employingthe CCD image sensor having the function of the electronic shutter forphotographing still images, the start timing of the effective lightexposure period tends to be delayed with respect to the shutter releaseoperating timing, so that the opportunity of shutter actuation tends tobe lost. In industrial application, if it is attempted to actuate thefunction of the electronic shutter in photographing an object conveyedon a transfer line, the start timing of the effective light exposureperiod is delayed, thus rendering it difficult to photograph the objectreliably.

Besides, with the electronic shutter function in the above-described CCDimage sensor, since shutter control is made by applying a shuttercontrol pulse to its substrate, a noise known as a shutter step(step-like fluctuations in substrate voltage caused by electronicshutter operation in each horizontal blanking period) is produced in aknown manner at a boundary of the shutter control pulse. Suchdeterioration in the picture quality is also produced by shutter stepwhen the CCD image sensor is used in a video camera.

The U.S. Pat. No. 4,984,002, assigned to the present assignee, has beenproposed for overcoming the aforementioned problem. In accordance withthis prior-art system, the time which elapses between application of atrigger signal until the next vertical synchronization signal is issuedis controlled for maintaining the constant start timing of the effectiveexposure interval.

It is noted that the video camera proposed in accordance with thepresent invention is frequently put to practical application, in whichcase it is frequently desired to supply external synchronization signalsto a video camera for synchronizing video signals thereto.

With the system of the U.S. Pat. No. 4,984,002, since the timing of thenext vertical synchronization signal is determined by the timing of thetrigger signal, video signals synchronized to the externalsynchronization signals can not be produced.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a solid state imagepickup apparatus whereby the start timing of the effective exposure timemay be maintained constant and whereby video signals can be producedthat can be synchronized with the external synchronization signals.

The present invention provides a solid-state image pickup apparatuscomprising a solid-state image sensor having a plurality ofphotosensitive elements arranged in a matrix of rows and columns foraccumulating electrical charges responsive to incident light thereon aplurality of vertical shift registers each coupled to a column of thephotosensitive elements for receiving electrical charges from thephotosensitive elements responsive to a sensor gate signal, memory meanscoupled to the vertical shift registers for receiving electrical chargesfrom the vertical shift registers responsive to a first transfer signal,horizontal shift register means coupled to the memory means forreceiving electrical charges from said memory means responsive to asecond transfer signal for outputting electrical charges from thesolid-state image sensor column by column, an overflow drain coupled tothe photosensitive elements for receiving electrical charges from thephotosensitive elements responsive to a shutter signal for draining theelectrical charges accumulated in the photosensitive elements in theirentirety, and driving means for supplying the shutter signal, sensorgate signal and the first and second transfer signals to the solid-stateimage sensor. The driving means supply the shutter signal to the imagesensor for draining any ineffective electric charges accumulated in saidphotosensitive elements, and the sensor gate signals are supplied afterthe lapse of an effective accumulating period after the supply timing ofthe shutter signal for transferring the effective electrical chargesaccumulated in the photosensitive elements to the vertical shiftregisters. The first transfer signal is supplied before the supplytiming of the shutter signal within a current vertical blanking periodso that the effective electrical charges transferred to the verticalshift registers responsive to the shutter signal issued during apreceding vertical blanking period are transferred to the memory means,while the second transfer signal is supplied during a period defined bythe supply timing of the shutter signal during the current blankingperiod and the supply timing of the first transfer signal supplied nextto said current shutter signal, so that the effective electric chargesare transferred to an output column by column.

Other objects and advantages of the present invention will becomeapparent from the following description of the preferred embodiments andthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the construction of a solid stateimage pickup apparatus according to an embodiment of the presentinvention.

FIG. 2 is a schematic plan view showing the construction of a frameinterline transfer CCD image employed in the solid image pick-upapparatus shown in FIG. 1.

FIG. 3 is a timing chart for illustrating the operation of thesolid-state image pickup apparatus shown in FIG. 1.

FIG. 4 is a timing chart for illustrating the operation of aconventional solid-state image pickup apparatus employing a solid-stateimage sensor having a function of an electronic shutter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, an illustrative embodiment of the presentinvention will be explained in detail.

The solid-state image pickup apparatus according to the presentinvention is arranged as shown for example in the block diagram of FIG.1.

The solid state image pickup apparatus, shown in FIG. 1, comprises a2-line readout type CCD image sensor 1, a signal processor 2 suppliedwith two lines of image signals read out simultaneously from the CCDimage sensor 1, an encoder 3 supplied with the image signals processedby signal processor 2, an output buffer 4 for outputting the videosignals outputted from encoder 3 at an output terminal 5, a CCD drivingcircuit 6 for driving the CCD image sensor 1, and a controller 7 forcontrolling the operation of these units 1 to 6.

The above CCD image sensor is a frame interline transfer (FIT) type CCDimage sensor comprising an image pickup unit IM which is a matrix arrayof photosensitive elements S, such as photodiodes, on an image pickupsurface, associated with pixels of odd-numbered fields and pixels ofeven-numbered fields, and an image storage unit ST to which electricalcharges produced by the photosensitive elements S are transferred viavertical transfer registers IMV_(REG), as shown in FIG. 2. That is, theimage sensor is a progressive scan (PS) CCD image sensor in which twolines of electrical charges produced by the photosensitive elements Sare read out simultaneously from the storage unit ST via two horizontaltransfer registers H_(REG1), H_(REG2) for outputting electrical chargesfor the totality of pixels, that is the pixels of one frame or twofields, as image pickup signals, for each field, by way of reading outtwo lines of the electrical charges simultaneously. With thisprogressive scan type image sensor 1, a smear drain VSD is provided viaa smear gate SMG along the horizontal transfer register H_(REG2) fordraining smear components. The PS type image sensor 1 having such smeardrain has already been put by the present Assignee to practicalapplication.

The signal processor 2 processes the image pickup signals for two linesread out simultaneously from CCD image sensor 1 with, for example, gammacorrection, to produce image pickup signals line by line which aresupplied to the above-mentioned encoder 3 where video signals conformingto the prescribed television system are generated from the line by-lineimage pickup signals supplied from the signal processor 2. The videosignals produced as an encoder output are outputted at an outputterminal 5 via a 75 ohms output impedance output buffer 4.

The controller 7 comprises a clock generator for generating systemclocks for the solid state image pickup apparatus, a synchronizationsignal generator g for supplying synchronization signals and blankingsignals to encoder 3, and a timing signal generator 10 for supplyingvarious timing signals to signal processor 2 and to CCD driving circuit6. The CCD driving circuit generates, based on timing signals suppliedfrom timing signal generator 10, a shutter control pulse φSP fordraining image pickup charges obtained from respective photoelectricconverting elements S in the image pickup unit IM to an overflow drain,sensor gate pulses φSG₁, φSG₂ for transferring image pickup chargesgenerated by the photosensitive elements S in the image pickup unit Imto vertical transfer registers IMV_(REG), vertical transfer pulses φIM₁to φIM₄ for vertically transferring signal charges in the verticaltransfer registers IMV_(REG) in the image pickup unit IM, verticaltransfer pulses φST₁ to φST₄ for vertically transferring signal chargesin the vertical transfer registers STV_(REG) in the storage unit ST, tohorizontal transfer registers H_(REG1) , H_(REG2), transfer pulses φVH₁,φVH₂ for transferring signal charges from vertical transfer registerSTV_(REG) in the storage unit to horizontal transfer registers H_(REG1)and H_(REG2), vertical transfer gate pulses φHHG for verticallytransferring signal charges from the first horizontal transfer registerH_(REG1) to second horizontal transfer register H_(REG2), smear gatepulses φSMG for opening the smear gate SMG for draining smear componentsin the smear drain VSD and horizontal transfer pulses φH₁, φH₂ forhorizontally transferring signal charges in the horizontal transferregister H_(REG1) and H_(REG2), to supply these pulses to the CCD imagesensor 1.

The controller 7 performs the following control operations: The solidstate image pickup apparatus performs an image pickup operation of 562.5lines/field and 60 field/second image pickup operation in conformity tothe high vision system. The synchronization signal generator 9 suppliesthe synchronization signals and blanking signals having the timing setin accordance with the high-vision system to encoder 3. On the otherhand, the timing signal generator 10 supplies various timing signals tothe signal processor 2 or to the CCD driving circuit 6 in a timedrelation with synchronization signals conforming to the high-visionsystem generated by the synchronization signal generator 9, as shown inFIG. 3.

At a timing t_(S) towards the end of the high-speed transfer during thevertical blanking period T_(VBLK), the CCD driving circuit 6 supplies asole shutter control pulse φSP to the substrate of the CCD imagesensor 1. This shutter control pulse φSP causes image pickup chargesgenerated in the respective photoelectric converting elements S in theimage pickup unit IM to be swept off in the overflow drain. The shuttercontrol pulse φSP is of a pulse width sufficient to sweep off the imagecharges in the photosensitive elements S in the overflow drain. Sincethe shutter control pulse φSP is generated in this manner at apredetermined timing within the vertical blanking period T_(VBLK)without dependency upon the shutter speed it is not responsible fordeterioration in the picture quality otherwise caused by the shutterstep.

After lapse of a predetermined exposure period T_(EXP) since the timingof the shutter control pulse φSP, the CCD driving circuit 6 suppliessensor gate pulses φSG₁ and φSG₂ to the sensor gate of the image pickupunit IM.

This causes image pickup charges accumulated in the photosensitiveelements S in the image pickup unit IM since the timing t_(S) of theshutter control pulse φSP to be transferred to the vertical transferregister IMV_(REG) at the timings SG₁, SG₂. That is, the image pickupcharges, obtained during a predetermined light exposure period T_(EXP),with the timing t_(S) of the shutter control pulse φSP as the lightexposure start timing, are transferred from the respectivephotosensitive elements S of the image pickup unit IM to the verticaltransfer register IMG_(REG). The start timing of the light exposureperiod T_(EXP), that is the effective charge accumulation period, is thetiming t_(S) of the shutter control pulse φSP and hence is constant.Meanwhile, FIG. 3 shows the sensor gate pulses φSG₁ and φSG₂ for thelight exposure period of 1/2000 sec, as well as showing the sensor gatepulses φSG₁ and φSG₂ for the light exposure period of 1/4000 second.

Besides, during the high-speed transfer period T_(AS) since timing t_(A)until t_(S) comprised within the vertical blanking period T_(VBLK), theCCD driving circuit 6 transmits high-speed vertical transfer pulses φIM₁to φIM₄ and φST₁ and φST₄ to the vertical transfer register IMV_(REG)and the vertical transfer register STV_(REG) of the storage unit ST.

This causes the image pickup charges transferred at the timings of thesensor gate pulses φSG₁, φSG₂ from the photosensitive elements S of theimage pickup unit Im to the vertical transfer register IMV_(REG) to betransferred from the vertical transfer register IMV_(REG) of the imagepickup unit IM to the vertical transfer register STV_(REG) of thestorage unit ST at an elevated transfer speed during the high-speedtransfer period T_(AS).

A high speed transfer period T_(BA) is provided ahead of the high-speedtransfer period T_(AS). During this high-speed transfer period T_(BA),the high speed transfer pulses φST₁ to φST₄ are supplied from the CCDdriving circuit 6 to the vertical transfer register STV_(REG) of thestorage unit ST. Opening the vertical transfer gate HHG by the verticaltransfer gate pulse φHHG during the high speed transfer periods T_(AS)and T_(BA), and also opening the smear gate SMG by the smear gate pulseφSMG causes ineffective charges in the vertical transfer registerSTG_(REG) in the storage unit ST to be swept off from the horizontaltransfer register H_(REG) via smear gate SMG to smear drain VSD whilecausing ineffective charges transferred at a high speed to the verticaltransfer register STV_(REG) of the storage unit ST during the high speedtransfer period T_(BA) to be swept off from the horizontal transferregister HE_(REG) via the smear gate SMG to the smear drain VSD duringthe next following high-speed transfer period.

During the normal transfer period T_(SB) excluding the high-speedtransfer periods T_(AS), T_(BA), the CCD driving circuit 6 transmits onevertical transfer pulse ST₁ to ST₄ for each H period, while transmittingtransfer pulses φVH₁, φVH₂, transmitting signal charges from thevertical transfer registers STV_(REG1) of the storage unit ST to thehorizontal transfer registers H_(REG1) and H_(REG2) at each H period tothe transfer gate, not shown. The signal charges transferred at a highspeed to the vertical transfer registers STV_(REG) of the storage unitST are read out during the ordinary transfer period T_(SB) via thehorizontal transfer register H_(REG1) and H_(REG2). During this readoutperiod, the smear gate SMG is opened.

The image pickup output signals, read out in this manner from thesolid-state image sensor 1, are supplied via signal processor 2 toencoder 3 and thereby encoded into video signals conforming to thehigh-vision system before being outputted at output terminal 6 viaoutput buffer 4.

Although the image pickup operation conforming to the high-vision systemhas been described in the foregoing it is also possible to generatevideo signals conforming to the NTSC system from the image pickupsignals read out from the CCD image sensor 1.

What is claimed is:
 1. A solid-state image pickup apparatus comprising:asolid-state image sensor having a plurality of photosensitive elementsarranged in a matrix of rows and columns for accumulating electricalcharges responsive to incident light thereon; a plurality of verticalshift registers each coupled to a column of said photosensitive elementsfor receiving electrical charges from said photosensitive elementsresponsive to a sensor gate signal; memory means coupled to saidplurality of vertical shift registers for receiving electrical chargesfrom said plurality of vertical shift registers responsive to a firsttransfer signal; horizontal shift register means coupled to said memorymeans for receiving electrical charges from said memory means responsiveto a second transfer signal for outputting electrical charges from saidsolid-state image sensor column by column; an overflow drain coupled tosaid photosensitive elements for receiving electrical charges from saidphotosensitive elements responsive to a shutter signal for draining theelectrical charges accumulated in said photosensitive elements in theirentirety; and driving means for supplying said shutter signal, saidsensor gate signal and said first and second transfer signals to saidsolid-state image sensor, said driving means supplying said shuttersignal to said image sensor for draining any ineffective electriccharges accumulated in said photosensitive elements, wherein said sensorgate signals are supplied after lapse of an effective accumulatingperiod since the supply of said shutter signal for transferringeffective electrical charges accumulated in said photosensitive elementsto said vertical shift registers, and wherein said first transfer signalis supplied before the supply of said shutter signal within a currentvertical blanking period so that the effective electrical chargestransferred to said vertical shift registers responsive to the shuttersignal issued during a preceding vertical blanking period aretransferred to said memory means, and said second transfer signal issupplied during a period defined by the supply of said shutter signalduring the current blanking period and the supply of the next transfersignal supplied so that the effective electric charges are transferredto an output column by column.
 2. The solid-state image pickup apparatusas defined in claim 1 wherein the supply timing of said sensor gatesignal is variable.
 3. The solid-state image pickup apparatus as definedin claim 1 wherein said sensor gate signal is alternately supplied bysaid driving means to an odd column and then to an even column of thematrix of said photosensitive elements.